The present invention relates to a process and a molding tool for the manufacture of molded parts having areas in the form of grids, grills or gratings (such as motor vehicle soft-faces, spoilers or bumpers) in which a fluid mass, and in particular a reaction mixture of reactive, fluid components is introduced into the cavity of a molding tool conforming to the molded part and fills this cavity.
Progressively more rapidly hardening systems, such as in particular those obtainable with polyurethane reaction mixtures are being adopted nowadays with a view to shortening the molding cycle. Thus, for example, when producing external parts for motor vehicles, such as front and rear spoilers, the cavities of molding tools must be filled within less than 2 seconds. This has led to the rule that in an area in the form of a grid, the reaction mixture always flows through along the ribs. Due to the asymmetric position of the sprue, however, this makes the flow paths unacceptably long and the density distribution in the molded part uneven. If the sprue is placed symmetrically, air inclusions are unavoidable due to the confluence of fluid which then occurs. Even in injection molding processes using conventional thermoplastics, difficulties in the form of air inclusions resulting from confluences occur when filling mold cavities due to the progressively more complicated forms of moldings.
The problem therefore arises of finding a process and a molding tool of the type indicated above in which air inclusions are avoided in the manufacture of the molded parts.